Insulating glass units are used in many industries to increase the thermal performance of items using glass (e.g., residential windows/doors/skylights, curtain walls, refrigerators, transportation vehicles, etc.). Most Insulating glass units include glass lites separated by a spacer along its perimeter, such that an air space is created between the glass lites, and most insulating glass units are hermetically sealed to maintain the airspace dry. A single insulating glass unit may contain multiple airspaces by sandwiching more layers of glass and spacers together.
The heat transfer properties (e.g., thermal performance) of an IGU may be compromised if there is a failure in the seal (e.g., a failure of the sealant to resist the ingress of moisture into the interior of the IGU). Additionally, a failure in the seal can lead to visual obstruction due to condensation/fogging on the interior of the IGU and the detrimental effects to the glass surface and/or coating from such repeated condensation effects. A failure in the seal can be due to, for example, manufacturing defects, contamination, environmental influences, chemical exposure, or the like. In addition, a contributor to seal failure can be a void in the sealant path, which can be caused by a sealant application error or a mishandling of the IGU during assembly.
Another failure that may compromise the heat transfer properties (e.g., thermal performance) of the IGU is stress cracks in the glass lites (e.g., complete and irreparable breaks in the glass lites). Various causes may lead to stress cracks, such as, for example, edge defects, improper handling, thermal stress, or the like. Edge defects may include microscopic factures at the edges of the glass, which create weak points for breakage to occur. Stress cracks may go undetected for long periods of time before a visible failure is observed. Therefore, although an IGU may be able to resist manufacturing, shipping, and installation processes, the IGU may fail from environmental stresses imposed on them by atmospheric and thermal influences after installation.
Various types of systems that use mirrors, cameras, and scanners have been used to inspect insulating glass units for manufacturing defects before they leave the manufacturer. In addition, human inspection is often performed to determine if there are any sealant defects or stress cracks in the glass lites, or if there is any edge damage in the unit that may lead to future stress cracks. However, the effectiveness of these inspection techniques is low, allowing defects to go undetected.